The present invention relates to a method for detecting, in an ink-jet image forming device, the presence/absence of ink in a detachable ink tank that has paths through which ink is supplied to ink-jet nozzles and for detecting the presence/absence of the ink tank.
In accordance with a conventional ink-jet print method, an image may be formed by ejecting ink on an on-demand basis. Print images have changed from monochromatic images to color images and, as color printing becomes more popular, a lot of image forming devices have detachably structured ink tanks, each for cyan, magenta, yellow, light cyan, light magenta, light yellow and black. Ink in those colors is stored in separate ink tanks. In general, an ink container that may be detachably mounted on an ink-jet head with ink jet nozzles provided thereon is called an ink tank, while a unit integrally composed of a head with an ink container is called an ink cartridge. In this specification, they are both called ink tanks.
Ink in those ink tanks is consumed differently and, the user must individually exchange exhausted ink tanks or replenish an exhausted ink tank through a path.
Japanese Patent Laid-Open Publication No. Hei 8-108543 and Japanese Patent Laid-Open Publication No. Hei 9-226149 disclose a technique wherein an optical reflector prism located at the bottom of an ink tank is combined with a reflective optical sensor to sense the ink.
With reference to FIGS. 1(a)-1(d), the principle of an ink sensing operation performed by the combination of the reflector prism and the reflective optical sensor will be described.
When a prism-structured ink sensor window is observed with a reflective optical sensor 33 composed of an emitter 21 and a receiver 22 of an infrared ray, the light from the emitter 21 does not reach the receiver 22 as shown in FIG. 1(a) if no object is present. Also, when a non-prism-structured object 23 is in the sensing position of the optical reflective sensor as shown in FIG. 1(b), the light from the emitter 21 does not reach the receiver 22 either. In addition, when liquid (ink) is present in the prism-structured part as shown in FIG. 1(c), the incident ray is refracted at the interface because of a refractive index between the prism-structured member (glass, polypropylene, etc.) and the liquid. At this time, the refractive index is represented by n (xcex1xe2x86x92xcex2)=sin xcex1/sin xcex2( greater than 1), where xcex1 is the incident angle and xcex2 is the refractive angle. As disclosed in Japanese Patent Laid-Open Publication No. Hei 7-164626, the refractive index (n) of air with respect to ideal gas is represented as n=about 1.0, the refractive index (n) of ink as n=about 1.4, and the refractive index (n) of polypropylene as n=about 1.5. Therefore, the polypropylene to ink refractive index n (polyxe2x86x92ink)=1.4/1.5≈0.93≈sin 68xc2x0/sin 90xc2x0, and polypropylene to air refractive index n (polyxe2x86x92air)=1.0/1.5≈0.67≈sin 42xc2x0/sin 90xc2x0.
This means that, when the polypropylene-to-ink incident angle is 68xc2x0, the refractive angle is 90xc2x0, that is, the incident ray is refracted in the direction of the interface vector at the interface between two objects (this incident angle is called the critical angle) and that, when the incident angle xcex1 greater than 68xc2x0, the incident ray makes a total internal reflection.
This also means that, when the polypropylene-to-air incident angle is 42xc2x0, the refractive angle is 90xc2x0, that is, the incident ray is refracted in the direction of the interface vector at the interface between two objects and that, when the incident angle xcex1 greater than 42xc2x0 (critical angle), the incident ray makes a total internal reflection.
Based on this principle, creating a prism-structured polypropylene ink tank container, whose incident angle of the infrared ray from the emitter 21 is 42xc2x0 less than xcex1 less than 68xc2x0, and installing the container as described above causes the light to refract when ink is present, and causes the light to make a total internal reflection when no ink is present. Therefore, when no ink is present in the prism-structured part as shown in FIG. 1(d), that is, when air is present there, a total internal reflection occurs and light from the emitter 21 reaches the receiver 22 to indicate that no ink is present.
However, when no ink tank is present on the holder (FIG. 1(a)), the same result is obtained as when an ink tank fully filled with ink is installed (FIG. 1(c)). Therefore, if no measure is taken, there is a possibility that, when no ink tank is present, the sensor senses that ink is present and, as a result, printing is done with no ink supplied to the print head (nozzles). This could damage the nozzles of the recording head of an ink-jet image forming device because of overheating, causing problems such as a head damage.
In view of the foregoing, it is an object of the present invention to provide an image forming device capable of detecting the presence/absence of ink, as well as whether an ink tank is mounted.
An image forming device according to the present invention for forming an image with an ink jet method comprises an ink tank detachable on a carriage; a prism disposed in the ink tank, the prism being covered with ink when the tank is filled with ink and being exposed when the tank is empty; an optical ink sensor that has a light emitter for projecting light onto the prism and a light receiver for receiving a reflected light of the projected light to detect a presence/absence of ink in the ink tank; and a reflector movable between a first position and a second position according to whether or not the ink tank is installed on the carriage, wherein the reflector, in the second position with the ink tank installed, reflects the light from the optical ink sensor back to the optical ink sensor and wherein the reflector, in the first position with no ink tank installed, does not return the light from the optical ink sensor back to the light receiver.
This allows an image forming device to detect the presence/absence of ink reliably, as well as a state regarding whether an ink tank is mounted.
The reflector comprises, with respect to the optical ink sensor, a reflective surface similar in function to the prism, and the optical ink sensor is used both to detect the presence/absence of ink and to detect the presence/absence of the ink tank. This configuration reduces the number of required parts.
The image forming device may further comprise an optical ink tank sensor for detecting a presence/absence of the ink tank such that separate sensors are used to detect the presence/absence of the ink and the presence/absence of the ink tank, the optical ink tank sensor including a light emitter for projecting light onto the reflector and a light receiver for receiving a reflected light of the projected light.
The configuration eliminates the need for the relative movement of the sensor with respect to the ink tank, allowing both ink and the ink tank to be detected at the same time. Providing separate sensors, one for each detection, increases freedom in the reflector configuration.
More specifically, the carriage may include an ink tank holder for holding the ink tank and a resilient member normally urging the movable reflector in one direction for placing the reflector in the first position, one end of the reflector being supported on the ink tank holder such that when the ink tank is installed in the ink tank holder, the reflector is pressed down against a resilient power of the resilient member to place the reflector in the second position.
The use of the resilient member enables the reflector position to be changed and, at the same time, allows the ink tank in the ink tank holder more securely.
The reflector may have a part with the same material and the same structure as those of the prism installed on an inside bottom of the ink tank.
The resilient member may be a plate spring formed by using a part of the reflector. Of course, a spring separate from the reflector may also be used.
The prism may be constructed and placed such that, a ridge line of the prism is parallel with a scanning direction of the carriage and when the ink in the ink tank reaches at least near an empty state, an interface between the ink and air moves on the ridge as the ink decreases. This allows the amount of ink to be detected.
Another image forming device according to the present invention for forming an image with an ink jet method comprises an ink tank detachable on a carriage; a prism disposed in the ink tank, the prism being covered with ink when the tank is filled with ink and being exposed when the tank is empty; an optical ink sensor that has a light emitter for projecting light onto the prism and a light receiver for receiving a reflected light of the projected light to detect a presence/absence of ink in the ink tank; a reflector provided on an outer surface of the ink tank; and an optical ink tank sensor that has a light emitter for projecting light onto the reflector and a light receiver for receiving a reflected light of the projected light to detect a presence/absence of the ink tank, wherein the reflector, with the ink tank installed, reflects the light from the optical ink tank sensor back to the optical ink tank sensor and wherein the reflector, with no ink tank installed, does not return the light from the optical ink tank sensor back to the light receiver.
This is a case wherein the reflector is provided on the ink tank itself. This reflector may record thereon information of individual ink tanks that are readable by the optical ink tank sensor.